In the production of contoured panels and parts utilized in aircraft or other large structures, it is desirable to securely hold a workpiece in order to perform precision machining or finishing operations. These operations may include, for example, cutting, drilling, trimming, and smoothing. Particularly in the aerospace industry, strong, lightweight workpieces made of composite materials are employed for an increasingly wider range and geometry of aircraft parts. In general, a composite material is typified by a structure of very strong fibers embedded in a softer matrix, for which the conventional machining techniques employed on metal parts may not be suitable. Instead, many machining or smoothing operations on composite workpieces employ high-pressure water jets guided by a numerically-controlled (N/C) machining system such as a multi-axis composite machining center (CMC) system. A CMC system typically directs gantry-mounted effectors to perform operations on a workpiece that is securely held by some form of holding fixture, which is positioned relative to an established reference frame.
Current holding fixtures are typified by a fixed machine bed, foundation, or platen, typically using pogo-type supports, to which linear actuators and other tooling devices are mounted. In turn, the workpiece is supported in the desired position by the linear actuators, while the effector (e.g., a high pressure water jet) moves about the gantry and acts on the workpiece. In general, current holding fixtures provide a fixed machine bed pattern having a limited number of tooling mounting locations available to support a limited number of tooling devices. In addition, a fixed machine bed pattern does not accommodate workpieces exhibiting a wider range of contours, geometries, and configurations, thereby inhibiting the future growth of part families. Moreover, in many present implementations, linear actuators are active, i.e., operate to set their respective height relative to the workpiece. Understandably, this type of linear actuator may be more expensive and complex to operate. In some cases, self-positioning by individual tooling may provide less accurate workpiece positioning due to the variability of errors among the array of tooling apparatus, and additional quality control equipment or processes may be needed. Therefore, current universal holding fixtures, as well as implementations attempting to address the aforementioned limitations, tend to be costly, complex, or both. There is a need for an universal holding fixture capable of supporting a workpiece during a manufacturing operation, capable of providing high-precision manufacturing operations using less costly tooling, and capable of accommodating workpieces exhibiting a wide range of contours, geometries, and configurations,